STIR Futures - Carry and Roll-Down

What is the best method to calculate your carry and roll-down from trading positions in stir futures, such as eurodollar spreads and flys? My first thoughts are there is no significant carry and that roll-down uses the assumption the curve does not change. Is this correct? Can anyone describe an example trade of how I would take a postion in the eurodollar futures curve to capture positive roll-down effects, and how this would be calculated? cheers for info.